The present invention relates to a mimeographic printing machine having a clamping means for clamping on a printing drum the leading edge of a mimeograph stencil paper wrapped around the outer peripheral surface of the printing drum, and more particularly to a mimeographic printing machine so designed that the stencil paper will be prevented from rising at the leading edge when released from the clamping means, and will be smoothly discharged thereafter.
In a general mimeographic printing machine of prior art having a stencil paper preparing device, the leading edge of a mimeograph stencil paper wrapped around the outer peripheral surface of a printing drum is clamped by an openable-closable clamp plate. The printing paper is carried into the apparatus in synchronization with the rotation of the printing drum, and printing is performed by transferring the ink to this paper through the perforating section of the stencil paper wrapped around the printing drum.
When a stencil paper is to be perforated by the use of a new original copy, the existing stencil paper on the outer peripheral surface of the printing drum is stripped off and this stripped stencil paper is ejected to a used stencil paper holding section, that is, stencil paper discharge operation is effected. This stencil paper discharge operation is carried out for example as follows. First, the clamp plate is opened to release the stencil paper. In this state, the printing drum is rotated to insert a stencil paper discharge craw into a stencil paper discharge position between the printing drum and the leading edge of the stencil paper raised from the outer peripheral surface of the printing drum. Thus the leading edge of the stencil paper is led between rollers, by which the stencil paper is stripped from the printing drum with the rotation of the rollers and is carried to be ejected out to the used stencil paper holding section.
In the prior art mimeographic printing machine in general use described above, the stencil paper wrapped around the printing drum is clamped at the leading edge having an edge nearly parallel with the direction of an axis of the printing drum by means of an openable-closable clamp plate which rotates on the center of a shaft parallel with the direction of the axis of the printing drum. A larger part of the stencil paper located on the delay side in the direction of a printing drum rotation is held on the outer peripheral surface of a the printing drum with the adhesion of the ink supplied through the opening provided in the printing drum.
Therefore, when the clamp plate is opened to release the leading edge of the stencil paper, the area ranging from the leading edge of the stencil paper to the opening area of the printing drum becomes free. This area of the stencil paper that has become free is curled (upward curl) in the direction in which the stencil paper goes away from the outer peripheral surface of the printing drum or is curled (downward curl) inwardly to approach the outer peripheral surface of the printing drum.
The curling direction of the free leading edge of the stencil paper depends upon several conditions explained below. First, the stencil paper is generally supplied in the form of roll, and the rolled condition of the stencil paper determines the curling direction. The stencil paper is a laminate of a thermoplastic synthetic resin film and a porous substrate. When this stencil paper is rolled, the curling direction is determined by whether a portion appearing on the outermost surface is the thermoplastic synthetic resin film or the porous substrate. Temperature and humidity changes can be the factors that determine the curling direction.
In the case of a large degree of upward curling, it becomes difficult to properly lead the leading edge of the stencil paper into the rollers, resulting in erratic discharge of used stencils. Also when the printing drum is rotated to discharge the used stencil paper with the leading edge curled upward, as the distance from the leading edge of the stencil paper to the opening area of the printing drum is longer and the printing drum rotation is faster, the leading edge of the stencil paper is raised larger by an air pressure, making it difficult to lead the leading edge of the stencil paper into a pair of rollers working as a used stencil paper conveying means.
Furthermore, when the leading edge of the stencil paper is largely curled downward, there exists no clearance between the printing drum and the leading edge, and therefore it is difficult to lead the leading edge by the stencil paper discharge craw into the rollers, thus causing a discharged stencil paper jam to occur. In order to solve the problem of the discharged stencil paper jam resulting from the presence of the downward curled leading edge or electrostatic adhesion of the stencil paper on the printing drum, there has been disclosed in Japanese Patent Publication No. Hei 4-69073 a raising member for raising the leading edge of the stencil paper when the clamp plate is opened. This raising member is designed to operate in connection with the opening and closing of the clamp plate; when the clamp plate is opened, the raising member rises in the vicinity of the leading edge to raise the leading edge off the outer peripheral surface of the printing drum, thereby providing a clearance between the outer peripheral surface of the printing drum and the raised leading edge of the stencil paper to thus prevent the adhesion of the stencil paper to the printing drum.
However, since the leading edge of the stencil paper raised by the raising member slips down to the delay side in the direction of the printing drum rotation, it becomes difficult to provide a clearance wide enough to insert the stencil paper discharge craw between the printing drum and the leading edge of the stencil paper. Consequently, the raising member alone is not fully effective to prevent the discharged stencil paper jam.